Diesel fuel may be delivered to customers with varying concentrations of biodiesel. Some diesel fuel may contain no biodiesel while other diesel fuel may contain 20% biodiesel. Consequently, a concentration of biodiesel in fuel stored on board a vehicle may change depending on fuel supplied to the vehicle during refilling and fuel stored on board the vehicle before refilling.
Biodiesel has a higher concentration of oxygen that is carried within the fuel as compared to fossil based diesel fuel. Biodiesel also has a lower energy density as compared to fossil based diesel fuel so that additional biodiesel may have to be supplied to an engine to produce an equivalent amount of power as compared to when fossil based diesel fuel is combusted. Consequently, when biodiesel is combusted in an engine, an increased driver demand torque to compensate for the lower energy content of biodiesel may increase boost pressure, injection pressure, and lower EGR amount, thereby increasing NOx emissions. Therefore, engine fuel economy and emissions may degrade if biodiesel in diesel fuel is not detected and compensated.
The inventors herein have recognized the above-mentioned disadvantages and have developed a method, comprising: adjusting an amount of fuel injected in response to a biodiesel concentration in fuel supplied to an engine; and adjusting an amount of fuel injected in pilot fuel injections and an amount of fuel injected in a main fuel injection in response to the biodiesel concentration, the amount of the main fuel injection increasing at a faster rate than the amount of fuel injected during the pilot fuel injections.
By adjusting an amount of fuel that is injected to engine cylinders and amounts of fuel that are injected during pilot and main fuel injections in response to a biodiesel concentration, it may be possible to reduce engine NOx emissions and improve fuel economy. In particular, a decrease in fuel economy and NOx emission observed when combusting biodiesel may be exchanged for an increase in particulate emissions which may decrease when combusting biodiesel. Further, urea may be conserved via when the method described herein is followed.
The present description may provide several advantages. Specifically, the approach may reduce engine emissions when biodiesel is combusted. In addition, the approach may also increase fuel economy as compared to operating an engine combusting biodiesel with conditions that are similar to combusting fossil based diesel fuel.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.